Road traffic congestion is a phenomenon that happens due to some sort of limitation on the normal flow of traffic. It is possible to divide congestion causes into two general groups: (1) recurrent overdemand, which happens on a regular basis (e.g. morning peaks due to commuters), and (2) sudden reduced capacity events, which include car accidents/breakdowns, infrastructural problems (e.g. road collapse, fire) or difficult weather conditions (e.g. fog, heavy rain/snows).
These two types of events are referred to as “incidents.” Incidents may result in losses of different kinds, including, for example, productivity losses due to commuter delays, as well as other losses such as injuries or deaths due to accidents or due to delays in responding to accidents.